Elan Corporation, plc (Elan) is a biotechnology company. The Company is focused on discovering and developing advanced therapies in neurodegenerative and autoimmune diseases. On February 6, 2013, the Company announced that it has entered into an asset purchase agreement with Biogen Idec to transfer to Biogen Idec all Tysabri IP and other assets related to Tysabri. As of 31 December 2012, there were approximately 72,700 patients on Tysabri therapy worldwide. On December 20, 2012, the Company completed the separation of a substantial portion of its drug discovery business platform (the Prothena Business) into a new, publicly traded company, Prothena Corporation, plc (Prothena). In December 2013, Perrigo Company acquired Elan Corporation Plc.